The narrator is an adolescent in the novel, Bob Starrett. He is an impressionable young man and looks up to his father, who is a strong, courageous man who believes in doing the right thing.
Enter Shane, a mysterious former gunfighter who has a mysterious past, and you've got every young boy's idol at the time. Shane is attempting to set his life right and leave his past behind him. Despite his gunfighting past, Shane is an honorable, courageous and "stand up" man who also believes in fighting for what is right. Because the narrator looks up to Shane and looks at him as a second father, he is naturally going to be a little biased in his portrayal of Shane.